Problems associated with the forging or counterfeiting of various types of documents are longstanding and well known. For example, forgery of negotiable instruments, currency or other documents of value is a continuing and ongoing problem to issuers of such documents.
Historically, attempts have been made to protect such documents by using special types of paper in combination with various printing techniques.
Techniques that have been developed include the use of papers which have optically discernible characteristics such as water marks. Alternately, the incorporation of planchets is well recognized in the creation of paper to be used for negotiable instruments. More recently, papers have been created that include detectable metal threads.
Printers have developed embossing techniques as well as techniques for the creation of randomly varying optically discernible characteristics which can be created during the printing process. Alternate printing techniques have included the use of special inks as well as the use of highly complex printed figures or graphics.
The verification and authentication problem extends to nondocumentary objects of value as well. For example the verification and authentication of paintings of substantial value can be a difficult, expensive and time consuming process. Similarly, the authentication of other types of nondocumentary objects which have value can also be an expensive and a time consuming problem.
Another example of objects of value where there is a continuing and ongoing authentication problem involves magnetic products such as computer disks and video tapes. Large scale and widespread copying of both of these types of objects results in substantial and ongoing losses to the producers of the authentic objects.
The widespread use of plastic credit or debit cards has created yet another set of authentication and verification problems. It is very common for such cards to include pre-recorded magnetic stripes which include transaction related information. This information can include account numbers, credit limits, and/or personal identification codes.
However, such cards have been especially susceptible to forgery in view of the fact that the magnetic encoding is almost always based on one or more publicly known standards. One such standard ANSI.times.4.16- 1983 is utilized in connection with many pre-recorded magnetic stripes associated with such cards.
Another class of documents which suffers from similar types of forgery and alteration problems includes transportation tickets . Airline tickets represent a particularly difficult problem in that the value of a ticket may vary over several orders of magnitude depending on the length of the trip and the destination. However, the issuing agency may use the same type of document for both inexpensive short trips as well as much more expensive long trips.
Multi-use documents, such as rail transportation tickets, present yet another type of authentication problem. Such documents are magnetically alterable at the time of use to decrease the remaining value of the card. However, if an original, unused document can be both physically and magnetically duplicated to create a usable counterfeit document, the issuing agency can lose substantial proceeds.
Various systems are known which can be utilized to create and authenticate verifiable documents or credit cards. Some of the known systems are optically based. Others are magnetically based.
One known type of system is disclosed in U.S. Pat. No. 4,423,415 issued to Goldman. The system of the Goldman patent makes use of the fact that paper documents have a randomly varying translucency characteristic. The randomly varying translucency is a natural characteristic which results from the process of manufacturing the paper.
In Goldman's system radiant energy, for example a beam of visible light, is directed at a selected portion of a document. The amount of light which passes through the document, as the document is being moved with respect to the beam, can be sensed. The document thus becomes a light modulator.
Because of the nature of the process of making the paper medium, no two documents will have the same variable translucency characteristic. As such, the sensed light which passes through each document can be used as a unique identifier of the document.
In accordance with Goldman's system, a representation of the sensed variable translucency characteristic is recorded on the document prior to use. When the document is placed into use, the variable random translucency characteristic is again optically sensed. The sensed characteristic is compared to the representation of the sensed characteristic previously pre-recorded on the document.
In the case of an authentic document, the translucency characteristic sensed at the time of use will correspond in a predetermined manner to the translucency characteristic pre-recorded on the document at the time of creation. A forged document on the other hand, based on a different piece of paper, will not have a sensed characteristic that corresponds to the pre-recorded representation unless the forger has a corresponding set of equipment and knows the details of creation of the authentic document.
A variation of the above described Goldman system is disclosed in U.S. Pat. No. 4,476,468. In this patent, also issued to Goldman, a light dispersing coating is deposited on a surface of a card or other document. Reflected light from the card is sensed and used to create a unique indicia for the document. This indicia can be recorded on the card for later verification purposes. The system of U.S. Pat. No. 4,476,468 can be used with opaque documents since it depends on sensing a reflected light beam. On the other hand, the system of the above-noted U.S. Pat. No. 4,423,415 requires a document which is at least in part translucent.
Alternate optically based systems are illustrated in U.S. Pat. Nos. 4,034,211 and 4,094,462 issued to Host et al. and Moschner respectively. The systems of the Host et al. and Moschner patents utilize a defraction grating affixed to an optically accessible portion of the card or document. Light reflected off of the defraction grating can be sensed and used to form a randomly varying document characteristic. This document characteristic can be encoded on the card for later verification purposes.
U.S. Pat. Nos. 4,114,032 and 4,218,674 both issued to Brosow et al. disclose systems which use fibers of a magnetic or a magnetizable material. The surface of the document can be coated with such fibers or the fibers can be added to the base material of the document when it is being manufactured. In accordance with systems of the Brosow et al. patents, the presence of the discrete magnetic fibers can be sensed over a portion of the document. The number of sensed fibers can be used as a document identifier. This number can be stored on the card for later comparison during the verification process.
U.S. Pat. No. 4,303,949 issued to Peronnet discloses a magnetically based verification system. The system of the Peronnet patent utilizes a magnetic stripe with a thickness that varies in discrete increments along the length of the stripe.
One way that is disclosed to form discrete thickness variations is to use a two layer stripe. One of the layers is a continuously extending layer. The other layer is a discontinuous layer applied above or below the continuously extending layer. At the time of verification, a signal is written to the multi-layer stripe. The resultant magnetization is then sensed. The physically permanent multi-layer structure results in a certain magnetization characteristic each time that the signal is applied to the stripe. The resultant magnetization characteristic can then be sensed in a read head. Then the stripe can be erased.
The Peronnet patent also discloses forming a stripe with discretely varying thickness increments by removing discrete amounts of material from a very thick stripe. This results in a stripe that has two or more regions with substantially different thickness. For example, the Peronnet patent refers to thickness increments greater than 40% of the base thickness.
U.S. Pat. No. 3,790,754 issued to Black et al. discloses a magnetic verification system that utilizes two different types of magnetic material. One type has a coercivity that is greater than the other type. According to the system of the Black et al. patent, in a preferred mode, two sets of magnetic ink are used to print interleaved bars having different magnetic characteristics. The bars can be sensed to form a digital number usable to identify the document.
While the known systems would appear to be effective with respect to verification of certain types of objects, each has certain limitations. The optically based systems require translucent or reflective surfaces. Many objects, such as credit cards, are not translucent. Other types of objects, such as disks or video tapes are not suitable for self-verification via the use of reflected light systems. Further, many types of products such as sports equipment or clothing do not have the necessary physical characteristics to utilize the known systems.
Known magnetic systems result in increased manufacturing costs and manufacturing complexity. In addition, special inclusions, modifications, magnetic regions or layers distinct from the normal read-write magnetic tracks are often needed.
Hence, there continues to be a need for an authentication/verification system of more general applicability to a variety of objects. Such a system preferably would be very inexpensive and would be integrally includable in the object without requiring that the object have particular physical characteristics.